Field of the Invention
The present invention generally relates to a variable magnetomotive force rotary electric machine that is used in vehicle motors and the like, and relates to a control device for the variable magnetomotive force rotary electric machine.
Background Information
A well-known example of a rotary electric machine used in interior permanent magnet motors (IPM motors) is disclosed in Japanese Laid-Open Patent Application No. 2008-295138). This Japanese Application discloses forming a plurality of flux barriers (layers having low magnetic permeability) on the q-axis magnetic path of the stator, providing a magnetic path on the d-axis such that Ld>Lq (where Ld is the d-axis inductance, and Lq is the q-axis inductance), performing strong magnetic-field control, and limiting the demagnetizing field in the permanent magnet to reduce the magnet volume.
However, in cases where these rotary machines are used in a high-rotation zone, the weak magnetic-field control is weaker than a typical flux-weakening interior permanent magnet (FW-IPM), but weak magnetic-field control is still needed, necessitating the use of expensive, high-coercivity magnets obtained by adding Dy (dysprosium) to a Nd—Fe—B alloy (where Nd is neodymium, Fe is iron, and B is boron).
From the perspective of variable characteristics, the rotary electric machine disclosed in Patent Literature 2 (Japanese Laid-Open Patent Application No. 2006-280195) has been proposed. However, a high-coercivity magnet and a low-coercivity magnet must be assembled together in this rotary electric machine, and this machine cannot be readily employed in cases where the supply of materials for the high-coercivity magnet is low. Additionally, problems have been presented in that the low-coercivity magnet is irreversibly demagnetized in high-load states, and strong magnetic-field control is therefore necessary to maintain magnetization, but in cases where it is not the case that Ld>Lq, a reluctance torque occurs in the opposite direction from the magnet torque, and efficiency therefore deteriorates in high-load zones.